Method in an electric net data transmission system for keeping the signal level constant in a coupling furnished with supply cable

ABSTRACT

Method in low voltage net transmission system for keeping the signal level of transmission constant on the net voltage rail or on wall outlet. In the method the feedback signals are taken wined or wirelessly from one or some locations of the actual apparatus or supply cable to the measuring and handling unit ( 60 ) of transmitting signals and further to the process unit ( 70 ) of sample and holding circuit (S &amp; H) or of corresponding means and control means (CONTROL), by which unit the control signal (U RC ) and/or U LC ) is taken to steer the output signal or output voltage of blocks ( 10, 20, 40  and/or  50 ) in a depending way from load impedance (Z LOAD ) and from the series impedance (Z W ) of supply cable (L W ) so that the amplitude (U LOAD ) of transmission signal level (U LOAD ) on voltage rail or some location of the supply cable or on wall outlet is constant or almost constant.

The common problem by data transmission in low voltage net for example12 VAC/DC, 24 VAC/DC, 48VAC/DC, 115 VAC, 230 VAC and 400VAC is theweakening of the transmission signal in the supply cable i.e. in thenetwork connection cable, for instance only a fraction of signals sentby the transmitter gets to the network phase rail. The problem is mostsevere when the supply cable is long and when the rail impedance at usedsignal frequencies very low. Among other things, this problem canprevent commercial profiting of net data transmission systems.

The invention removes the problem in eliminating the impact of theweakening on coupling capacitor C_(c) and of supply cable L_(W), Z_(W).Thus the standard-allowed maximum signal SFS-EN-50065-1:122 dBuV isproduced in the network rail and in this respect data transmission in alow voltage net is made reliable even with low net impedance Z_(LOAD).

Even in most advanced solutions of present technique, where the outputsignal of the apparatus is constant, in other words independent of thenet impedance, the coupling capacitor Cc and supply cable causeweakening of the transmission signal. The situation is especially bad,when the net impedance is very low.

FIG. 1 shows the weakening of transmission signal by a 3 meter supplycable. Thereby the weakening is about 7 dB, but the length of supplycable being for instance 10 m the weakening is even 14 dB (⅕ voltage)when the load impedance of net impedance Z_(LOAD) is 1 ohm.

The block diagram of the invention is presented in FIG. 2. Block 10 isthe source of operating voltage furnished with constant or adjustableoutput voltage U_(S). U_(S) is the operating voltage of signal amplifier20.

Input signal U_(IN) (e.g. under 95 kHz, 95-125 kHz, 125-140 kHz or140-148.5 kHz) can be a sinus or a square signal to its amplitude e.g. 5V_(pp). The input signal is taken by adjustable amplification or, aftersignal amplifier 20, furnished with level regulation U_(OUT) to low passor band pass filter 40, where harmonic (crack) signals are filtered outfrom the basic frequency signal. Filtered signal U_(FL) is then taken tocoupling unit 50 in the network and further to the low voltage net L-Ne.g. with a 3 meter supply cable.

The network impedance between phase rail and zero rail, rail impedance,is described by signal frequencies with load impedance Z_(LOAD). Theseries impedance is described with impedance Z_(W). The supply cablelength is _(LW).

Dotted broken line A illustrates the traditional idea of thetransmitting apparatus, which has an output connector O reference n r.51: L-N. Dotted broken line B illustrates an expanded idea of thesending apparatus according to this invention. Then the supply cable isa fixed part of the apparatus and the output coupling of the apparatus,expanded as per this idea, is the supply cable ends 1-n to be connectedto the phase and the zero rail. The supply cable length must be of priorart as well as its electric and other properties.

The basic idea of this invention is that a supply cable of certainlength and type L_(W), Z_(W) is a fixed part of the transmissionapparatus and between cable ends 1-n, coupled to the network phase railand zero rail, the rail voltage is kept constant by means of feedbackcoupling. The output coupling L-N of the transmitting apparatus is atthe same time a phase and zero rail connection. In this way thetransmission signal U_(LOAD)/Z_(LOAD) amplitude U_(LOAD), which must beput in between phase and zero rail, is constant.

The intern generator impedance of the signal generator, formed bytransmitter and connecting cable, can in this way be formed almost to arate of 0 ohm measured in the voltage rail or wall outlet connection.

The invention is not in contradiction for instance with standard SFS-EN50065-1, since the signal voltage U_(LOAD) in voltage rail or in walloutlet does not under no circumstances exceed the allowed rate 122 dBuV.The same result could be reached also without the invention if thelength of supply cable would be, for instance, only 10-20 cm. Generally,in practice it would, however, be impossible.

Operation Alternative 1 BLOCKS 60 and 70

Steered before actual data transmission by micro processor _(U)Pincluded in block 70 the signal amplifier 20 sends a reference levelsignal of brief duration, e.g. 40 ms, in such a way that the signalamplifier always receives its constant control voltage U_(RC)(RC=REFERENCE CONTROL) from the sample/holding/steering block 70. Thelevel of U_(RC) is such kind that from a load impedance Z_(LOAD)=50 ohma transmission signal U_(LOAD) in size of e.g 3.56 V_(PP) would bereached. U_(LC) is out of function.

During transmission the load impedance (network rail impedance) Z_(LOAD)is what it happens to be at that moment. Block 60 measures thetransmission signal Ua from block 20, U_(B) from block 40 or U_(C) fromblock 50 and U_(D) from block 50. The transmission signal voltage Ua, Ubor Uc is the lower the lower Z_(LOAD) is. In block 50 of signaltransformer T_(C) the primary current I_(C) is measured by measuring thesignal voltage U_(D) R=0.5 ohm exceeding the series resistance. I_(C) isthe higher the lower the Z_(LOAD) is.

Alternatively instead of above Ic of signal current it is also possibleto measure the secondary current I_(LOAD) of the signal transformerT_(C), which current runs through coupling capacitor C_(C) to supplycable and further to load impedance Z_(LOAD). The signal voltage U_(D)to be measured is proportional to signal current Ic or I_(LOAD). If theI_(LOAD) is measured by measuring U_(D) and/or U_(C) the couplingcapacitor T_(C) is measured from the secondary side before or after thecoupling capacitor C_(C), still a separate coupling unit is needed forcoupling of signals Ud and Uc to block 60.

Alternatively signal voltage Ud can instead of block 50 be measured fromblock 20 or 40. Signal voltage Ud gives information of signal currentI_(LOAD) in transmission situation.

The phase angle Ø between Ua,Ub,Uc and Ic depends on the phase angle ofZ_(LOAD), in other words in what extent the Z_(LOAD) is resistive,capacitive or inductive. Block 60 includes a phase difference detectorand signal handling elements and a lot of screening. On basis of abovedata in block 60, for instance, following variables are calculated:

-   -   Z=Ua/Ic, Ub/Ic or Uc/Ic ohm        -   Z/Ø=Z    -   Ø=(Ua, Ic or Ub Ic or Uc, Ic)

Impedance Z is a kind of a virtual impedance, on basis of which absolutevalue Z and on basis of phase angle Ø data of the Z_(LOAD) absolutevalue and phase angle is received

In block 60 direct voltages U_(Z) and U_(Ø) proportional to measuredimpedance Z and phase angle Ø are formed and taken to block 70 to themicroprocessor that by means of U_(LC) memory map transforms them intocontrol voltage to steer the amplifications or levels of signalamplifier 20 into such state that into load impedance Z_(LOAD) atransmission signal 3.56 V_(PP) or 122 dBuV, constant to its level, isproduced. U_(LC) remains in the holding circuit of block 70 till afterabout 1-4 seconds it gets removed by a new U_(CL) value determined bythe next new reference measuring (LC=LEVEL CONTROL).

All in all, always, for instance for 40 ms, the apparatus sends atransmission signal according to certain reference level, for instanceat intervals of 1-4 ms. During the mentioned 40 ms a virtual impedanceZ=Z/Ø proportional to the size and phase angle of load impedanceZ_(LOAD) is determined, the variables U_(Z) and U_(Ø) determined bywhich pick from the U_(LC) memory map an U_(LC) control voltagecorresponding to them in order to regulate them to such a state that theU_(LOAD) of the transmission signal level is 3.56 V_(PP) with the loadimpedance in question.

Alternatively, for the above presented virtual impedance method (Z∠Ø)the control voltage U_(LC) of signal amplifier 20 can be formed simplyby means of transmission signals Usa, Ub or Uc, and by means of Udamplitude monitoring.

The transmitting apparatus, reckoned from signal amplifier 20 andadvancing through the low pass and/or band pass filter 40 and thenetwork of block 50 to the supply cable and finally further to the loadimpedance Z_(LOAD), includes capacitors, resistances, minithrottles, atransformer and other inductances and capacitors. Accordingly, by meansof different load impedance Z_(LOAD) values it is possible to measurefrom different locations in the apparatus transmission signals ofdifferent size (Ua,Ub,Uc,Ud) as to their amplitude. For instance, onbasis of amplitude combinations of two transmission signals, as Ub andUd, the size and nature of load impedance Z_(LOAD) can be concluded. Itis the question of an amplitude method as an alternative to the virtualimpedance method.

FIG. 2: Block diagram of the invention and FIG. 6: U_(LC) memorymap=U_(LC) (Z, Ø). With control voltage U_(LC) it is possible inaddition to block 20 or alternatively to control block 40, 50 and/orblock 10. The same also concerns control voltage U_(RC).

Operation Alternative 2 Blocks (80 and 90)

Feedback coupling is taken from the phase and zero rail (rail voltage) 1_(LOAD)-n_(LOAD) or for example from wall outlet through coupling unit80 to the ALC/ALG block 90, where control signal U_(ALC) or U_(AGC) orU_(ACC) is formed to control the level of signal amplifier 20 or theamplification formed to such a state that the level U_(LOAD) of thetransmission signal is constant, in other words independent of the loadimpedance Z_(LOAD).

ALC=Automatic Level Control

AGC=Automatic Gain Control

ACC=Automatic Cutting Control

Control voltage U_(ALC), U_(AGC) and/or U_(ACC) can in addition to block20 or alternatively control block 40, 50 and/or block 10. The same is inquestion also with control voltage U_(RC).

The net work connecting unit, input unit 50 and the output unit 80include in case of galvanic separation a coupling transformer T_(C) andT_(CC) and a coupling capacitor C_(C) and C_(CC) and possibly also othercomponents. There, is in a so called direct coupling no galvanicseparation, from the network and the coupling units 50 and 80 can intheir simplicity include only a coupling capacitor C_(C) and C_(CC).

A Practical Application. FIG. 3

FIG. 3 shows a practical application of the invention. The operatingprinciple is already described above. In connection with U_(LC) memorymap, FIG. 6, it can be stated that it presents the control voltagevalues U_(LC) of the signal amplifier corresponding to 304 differentload impedance Z_(LOAD) values, by means of with it is then possible tobring about to the load impedance in question a constant signaltransmission voltage U_(LOAD) 3.56 V_(PP) or 122 dBuV. In addition tothe Z_(LOAD) of impedances it presents the Z=∠Ø values Z and Ø of themeasured virtual impedance, as addresses of the storage location, andthe U_(LC) value as content of said storage location. The virtualimpedance Z is, in addition to block 50, also affected by block 20 and40 preceding it and by the supply cable. Accordingly, the virtualimpedance does not give any good linear picture of load impedanceZ_(LOAD) especially in so far as the phase angle Ø is concerned. This isdue to the fact that from signal amplifier 20 to load impedance Z_(LOAD)there are throttles, a transformer, capacitors and a supply cable, bythe interaction of which there are phase distortions as well as bydifferent resonance effects. One brilliant idea of the invention is thatits above mentioned circumstances are of no importance at all, since itis enough that the virtual impedance in some way depends only on theZ_(LOAD) and the supply cable and only in some way differing virtualimpedance values Z and Ø are produced and by this means U_(LC) memorymap addresses Z and Ø. Then into appropriate storage location such acontrol voltage value U_(LC) of the signal amplifier is stored that bymeans of it a proper output voltage U_(OUT) of signal amplifier and aconstant transmission signal (rail signal) U_(LOAD) to the appropriateload impedance Z_(LOAD) is produced.

The invention functions by dotlike frequencies or by a certain frequencyband. An U_(LC) memory map is always needed for frequencies or frequencybands far enough from one another and for different supply cables. Ifthe virtual impedance is not exactly the same as some storage locationaddress, the closest or a more proper address is chosen.

In the U_(LC) memory map there can be more or even less than 304 storagelocations. In practice a whole swarm of memory maps may be needed. If asufficient amount of supply cables of different length and type are usedand with frequencies or frequency bands fair enough from one another foreach case an own U_(LC) memory map is needed. Instead of the 3 m lengththe supply cable can be even longer, but then the it may be necessary toincrease the operating voltage of signal amplifier 20.

The value tolerances of the transmitter components must be small enoughprecision components or then by each entire transmitter unit an U_(LC)memory map is programmed in a special programming location individuallyby serial production. This applies to this and the next practicalapplication.

Another Practical Application of the Invention. FIG. 4

Instead of the virtual impedance method the amplitude method can be usedin order to generate a control voltage U_(CL). In the amplitude methodit is possible to determine, on basis of two, for instance Ub and Udsignal voltage amplitudes, from the U_(LC) memory map U_(LC)=U_(LC) (Uband Ud) a control voltage U_(LC) corresponding to load impedanceZ_(LOAD) can be determined, which regulates the signal amplifier outletvoltage U_(OUT) as to its amplitude to such state that rail signalU_(LOAD)/Z_(LOAD) is constant as to its level, in other words 3.5 V_(PP)or 122 dBu V. Quite clear differences have been measured for Ub and Ud,when Z_(LOAD)=1-50 ohm and Ø_(LOAD)=0-±90°:_Ubmax−Ubmin=6 V_(pp) andUdmax−Udmin=310 mV_(pp)/0.5 ohm. The Ub and Ud amplitude can be measuredby A/D transformer (10 and 8 bits) during transmission of an ohm signal3.56 V_(pp) of reference level, for instance 40 ms/1-4 seconds. The bitfigure 10+8 received from A/D transformer, corresponding to Ub and Ud,can function directly as address of memory map, from the storagelocation indicated by it, a control voltage, proper for the situation,is reached for U_(LC) signal amplifier 20 by means of the holdingcircuit in block 70. From U_(LC) memory map the closest or more properaddress is chosen if the measured address is not exactly the same.Instead of the A/D transformer comparator degrees can be used to measurethe Ub and Ud levels of transmission signals by steps.

The U_(LC) memory map presented in FIG. 6 is suited also for thispractical application and if the address co-ordinates Z and Ø of thestorage locations are correspondingly transformed into Ub and Ud.U_(LC)=U_(LC)(Ub,Ud).

A third practical application of the invention. FIG. 5.

FIG. 7 shows of this practical application transmission signal levelU_(LOAD) (1) with feedback coupling and without feedback couplingU_(LOAD) (2) as function of load impedance (rail impedance) Z_(LOAD).FIG. 7 shows the signal levels of FIG. 5 practical application. Thetransmission signal of the real apparatus is U_(W)+U_(LOAD) in netconnector (51) with feedback coupling.

Previously known is that the longer the supply cable L_(W),Z_(W) of thetransmitter of a data transmission system in a low tension net, and thelower the impedance by signal frequencies in the supply cable other end(load impedance or rail impedance) Z_(LOAD), the lower the voltage levelU_(LOAD) of the transmission signal.

However, previously no effective means are known how to eliminate thestrong weakening of signal caused by above mentioned circumstances. Theproblem does not vanish in that the transmitter maintains to keep thesignal level constant in its output connector.

Operation Alternative 1:

In transmission situation signal (U_(OUT) block 20) of certain levelreference is sent repeatedly but briefly and during that time one ormore transmission signals Ua,b,c . . . Un are measured from differentlocations of the transmitting apparatus (apparatus+supply cable), bymeans of which signals amplitudes, phase shift keying, proportions,multiplies, sums and other features of the output signal is regulatedthe blocks 20, 40, 10 and/or 50 in the transmitter directly or by meansof control signals (block 60 and 70) to such a state that the amplitudeU_(LOAD) of the rail signal U_(LOAD) is constant, in other wordsindependent of load impedance Z_(LOAD) till the transmission of the nextreference level signal. Signals Ua-Un, U_(Z), U_(Ø), U_(RC), U_(LC),U_(ALC), U_(ACC) and U_(AGC) can instead of the voltage signal becurrent signals, frequency signals, code signals, electric fieldsignals, magnet field signals, optical signals, electromagnetic signalsand/or signals of other possible types.

Operation Alternative 2:

In transmission situation the feedback signal is taken directly from therail impedance Z_(LOAD) poles or near the poles (usually from the phaseand zero rails). The feedback signal is brought to output signal 80 byseparate conductors further to ALC/AGC/ACC block 90, where controlvoltage U_(ALC), U_(AGC) and/or U_(ACC) to be produced, is taken tocontrol the output or voltage signal of block 20, 40, 10 and/or 50 tosuch state that the amplitude U_(LOAD) of rail signal U_(LOAD) isconstant or almost constant.

1. Method in low voltage net data transmission system for keeping thesignal level of transmission constant on the net voltage rail or forexample in wall outlet or in other corresponding connecting point or insphere of influence by data transmission furnished with a supply cable,in which method the coupling means for making said signal voltageconstant comprise:—operating voltage source (Us) for the signalamplifier (10),—signal amplifier (20),—low pass or band pass filter(40), network connecting unit (50),—supply cable, length (L_(W)),—seriesimpedance (Z_(W))—measuring and handling unit (60) of the transmittedsignals for the storage location determination,—electronic unit (70)including sample and holding circuit (S&H) and control circuits(CONTROL) to produce control signal (U_(RC) and/or U_(LC)) by means of(U_(LC)) memory map or by means of other type signals, characterized inthat in the method the feedback signal(s) is taken wired or wirelesslyfrom one or some locations or sphere of influence of the actualapparatus or supply cable (L_(W)) to the measuring and handling unit(60) of transmitting signals and further to the process unit (70) ofsample and holding circuit (S&H) or of corresponding means and controlmeans (CONTROL), by which unit the control signal (U_(RC)) and/orU_(LC)) is taken to steer the output signal or output voltage of blocks(10, 20, 40 and/or 50) in a depending way from load impedance (Z_(LOAD))and from the series impedance (Z_(W)) of supply cable (L_(W)) orpossible from frequency, so that the amplitude (U_(LOAD)) oftransmission signal level (U_(LOAD)) on voltage rail or some location ofthe supply cable or on wall outlet or on corresponding connecting pointis constant or almost constant.
 2. Method according to claim 1characterized in that in the method a reference transmission signal(U_(OUT) constant/block 20) of brief duration, e.g. 40 ms, is sent andby means of feedback signals measured from different points on thetransmitter and/or supply cable from a drawn up (U_(LC)) memory map acontrol voltage is determined, by means which voltage the output levelof signal amplifier (20) reaches at a predefined value so that thetransmission signal (U_(LOAD)) is in voltage rail or in wall outlet orin other corresponding connecting point constant or almost constant. 3.Method in low voltage net data transmission system for keeping thesignal level of transmission constant on the net voltage rail or on somelocation of the supply cable or in sphere of influence of the rail orcable or in wall outlet or in other corresponding connecting point, inwhich method the coupling means for making said signal voltage constantcomprise:—operating voltage source (Us) for the signal amplifier(10),—signal amplifier (20),—low pass or band pass filter (40), inputunit (50),—supply cable, length (L_(W)), series impedance(Z_(W)),—output unit (80) or unit adapted to the function,—ALC/AGC/ACCunit (90) to bring about control signals U_(ALC), U_(AGC) and/orU_(ACC), whereby the output signals and control voltages of blocks (10,20, 40 and/or 50) can be steered by control signal U_(ALC), U_(AGC)and/or U_(ACC), characterized in that in the method the rail signal(U_(LOAD)) or close to voltage rails influencing signal in transmissionsituation, or from one or some locations of the supply cable (L_(W)),the feedback signal is taken wired or wireless by means of output unit(80) or by other way to (ALC/AGC/ACC) unit (90) to bring about controlsignals, by means of which the blocks (10, 20, 40 and/or 50) is steeredfrom load impedance (Z_(LOAD)) and supply cable, length (L_(W)) and theseries impedance (Z_(W)) and possible frequency, by a depending way sothat the amplitude of transmission amplitude level (U_(LOAD)) isconstant or almost constant on the voltage rail or some location of thesupply cable or in wall outlet or in other corresponding connectingpoint.